Well I think they will announce something at the incoming TGS. I'll be shocked if they weren't working on something new all this time since XIII's release.
Let's hope so... TGS sounds like the best bet right now.
Either TGS 2012 or the 50th Amusement Machine Show would be a great bet for SNK to announce something. Also, I wouldn't call UM a KOF XIII update because its a canon game, and that stuff only applies to dream matches.
But hey, I wouldn't mind them pulling a BlazBlue: Chrono Phantasma for KOF (subsystem and gameplay overhaul).